1. Field of the Invention
The present invention relates to an optical pickup apparatus, and more particularly to an optical pickup apparatus for recording/reproducing information on/from a magnetooptical recording medium which is capable of overwriting.
2. Description of Related Art
In recent years, a method to record information on a magnetooptical recording medium capable of over-writing has been devised as a recording method using a rotary-type optical recording head.
As the method for the over-writing, there are a method utilizing a magnetic field modulation system and a method according to a light modulation system.
Optical disk has been widely known as a recording medium for recording/reproducing an audio signal and a video signal. The optical disk has a capability to achieve a high recording density. However, its area which can be used for recording is small, so that a limitation is posed on its overall recording capacity.
Alternatively, there is a tape-shaped recording medium such as the magnetic tape used for a VTR (Video Tape Recorder) and the like. Although it is inferior to the optical disk in terms of recording density, the tape-shaped recording medium is capable of recording a quantity of information one hundred times that of the optical disk, and superior than the optical disk in terms of the recording capacity. Therefore, by combining a high recording density characteristic of the optical disk and a large recording capacity characteristic of the tape-shaped recording medium, a recording medium having a small size and also a large recording capacity can be realized.
Recording/reproducing of the information onto/from either the tape-shaped recording medium or a card-shaped recording medium (hereinafter referred to as an optical card) has been heretofore examined using a laser beam, in which a magnetooptical recording film such as TdFeCo is formed on a base film like a magnetic film.
A configuration of a conventional picking-up apparatus for recording/reproducing information onto an optical card is schematically shown in FIG. 1 by way of an example of a write once type apparatus.
As shown in FIG. 1, the conventional pickup apparatus consists of a signal generation circuit 16 which converts an input signal SR to a recording signal SR1 by performing signal processing for the input signal SR using a signal processing part 1, outputs it to a stationary optical part SOP, and performs signal processing for a reproducing signal from the stationary optical part SOP to output a reproducing signal SP, said input signal SR being supplied from the outside to be recorded; the stationary optical part SOP which makes light beam B for recording information onto an optical card 24 at the time of the recording of information in response to the recording signal SR1, said stationary optical part SOP including a light receiving device which receives reflection light of the light beam from the optical card 24 at the time of the reproduction of information and outputs a reproducing signal SP, a rotary optical part ROP which converges the light beam B onto the optical card 24 at the time of the recording of information while rotating around a straight line perpendicular to a recording surface of the optical card 24, said light beam B being emitted from the stationary optical part SOP, and serves to guide the reflection light of the light beam B from the optical card 24 to the stationary optical part SOP at the time of the reproduction of information: a conversion gear 26 which transports the optical card 24 together with a tray 25 holding to mount the optical card 24 in a longitudinal direction of the optical card 24 at a constant speed, thereby changing a positional relationship relative to the rotary optical part ROP; relative position changing device including a transportation motor 27 having a gear engaged with the conversion gear 26; and a magnet 28 to apply a magnetic field to the optical card 24 at the time of the recording of information.
The stationary optical part SOP consists of a laser control part L which outputs a laser driving signal SD to control the light beam B emitted from a laser diode 7 depending on the recording signal SR; a laser diode 7 which emits the light beam B depending on the laser driving signal SD; a beam splitter 9 which reflects a part of the light beam B from the laser diode 7 to guide it to a monitoring detector 4 incorporated in the laser control part L and the other part thereof passes therethrough to guide it to an actuator 11, and reflects the light beam B reflected by the optical card 24 to guide it to the light receiving part D; the actuator 11 which includes a lens to adjust a position of the light beam B such as tracking control and focus control for the light beam B and a driving part for the lens; a light receiving part D which receives the light beam B reflected by the beam splitter 9, generates a reproducing signal SP in response to the light beam B to output it, and generates a beam position adjusting signal (error signal) such as a focus error signal and a tracking error signal to emit it; a servo control circuit 17 which generates a driving signal for the actuator 11 in response to the beam position adjusting signal; a system controller 5 which a driving command to a laser driving circuit 2 and the servo control circuit 17 if necessary; and motor control device 6 which control a rotation of a rotation motor 23 using pulse signals (FG and PG) supplied from position signal generation device 18 of the rotary optical part ROP so that its rotation speed is made constant.
It should be noted that a collimator lens 8 is used to convert light emitted from the laser diode 7 to parallel light and a relay lens is used to converge the light beam to the actuator 11 and also to convert the light beam from the actuator 11 to parallel light.
The laser control part L consists of a recording circuit I which performs modulation processing for the input signal SR to output the recording signal SR1; the monitoring detector 4 which receives the light beam B reflected by the beam splitter 9 to output a monitoring signal SM; an APC (an Automatic Power Controller) 3 which outputs a monitoring control signal SR2 to control the light beam B depending on the monitoring signal SM; and a laser driving circuit 2 which outputs the laser driving signal SD to drive the laser diode 7 depending on the recording signal SR1 and the monitoring control signal SR2 when the driving command is made by the system controller 5.
The light receiving part D consists of a cylindrical lens 12 which provides the reflected light of the light beam B with astigmatic aberration in order to obtain a focus error signal used for focus control of light beam B from the optical card 24, the reflected beam of the light beam B being reflected from the optical card 24 by the beam splitter 9; a polarization beam splitter (PBS) 13 which passes polarization light therethrough, the polarization light having a predetermined polarized state included in the reflected light of the light beam B which is provided with the astigmatic aberration, and reflects other polarization light; a light receiving element 15 which receives the polarization light reflected by the PBS 13; a light receiving element 14 which receives the polarization light passing through the PBS 13; and a signal generation circuit 16 which generates the reproducing signal SP, the tracking error signal TE and the focus error signal FE depending on detection signals output from the light receiving elements 14 and 15.
The rotary optical part ROP consists of reflection mirrors 19 and 20 which serve as light beam guiding device for guiding the light beam emitted from the stationary optical part SOP to an objective lens 21 and form an optical path to guide the reflected light of the light beam B from the optical card 24 to the stationary optical part SOP; the objective lens 21 which converges the light beam B onto a recording surface of the optical card 24; a rotating motor 23 which rotatively drives a rotary drum 22 mounting the reflection mirrors 19 and 20 together with the foregoing light beam guiding device and the objective lens 21, the light beam guiding device and the objective lens 21 being driven rotatively thorough the rotary drum 22; and positional signal generation device 18 which generates a pulse signal as a positional signal indicating the rotation position of the rotary drum 22, the pulse signal being output in synchronization with the rotation of the rotating motor 23.
The position signal generation device 18 consists of first projection portions 181 of rectangular-shape to detect a rotation speed of the rotary drum 22, which are radially arranged at intervals of a first predetermined angle, for example, 45 degrees; second projection portions 182 arranged at intervals of a second predetermined angle, for example, 360 degrees, in a rotation axis of the rotary drum 22 against the first projection portions 181; a photo interrupter 183 provided so as to pinch the first projection portion 181 in a rotation axis direction; and a photo interrupter 184 provided so as to pinch the projection portion 182 in the rotation axis direction.
Each of the photo interrupters 182 and 184 consists of a pair of a light emitting element and a light receiving element and is fixed to a fixing portion having no relation to the rotation of the rotating motor 23. Therefore, when each of the foregoing projection portions 181 and 182 passes between the light emitting element and the light receiving element of the photo interrupter in accordance with the rotation of the rotating motor 23, the projection portions 182 and 182 shield the light from the light emitting elements whereby the pulse signals in response to the position of the projection portions are output from the light receiving element.
For example, when the first and second predetermined angles are set to 45 and 360 degrees, respectively, one pulse is obtained from the photo interrupter 183 each time the rotating motor 23 rotates by 45 degrees specifically, the pulse signals of eight pulses are obtained from the photo interrupter 183 every one rotation of the rotating motor 23 and the pulse signal of one pulse is obtained every one rotation thereof. Therefore, by counting the pulse signal (FG) output from the photo interrupter 183 triggering the pulse signal (PG) from the photo interrupter 184, the rotation position of the objective lens 21 can be detected from the count value.
By the pickup apparatus having the above described configuration, at the time of the recording of information, information is recorded while forming arc-shaped recording tracks on the optical card 24. Moreover, at the time of the reproduction of information, the recorded information is read out by the light beam B irradiated onto the optical card 24 so as to follow the recording track. In this summarized example, the write once type is used, the optical card 24 is a formatted one, and recording of information can be performed only once.
Next, a recording/reproducing operation of a picking-up apparatus capable of over-writing will be described using FIG. 2.
Referring to FIG. 2, a magnetooptical recording medium 141 composed of a recording layer formed of a magnetic thin film and an auxiliary layer, both of which are not shown in FIG. 2, is rotatively driven by a magnetooptical recording medium rotating device 142 and recording/reproducing of signals is carried out by laser beam converged by an objective lens 147. The laser beam is generated by a laser beam light source 150. At the time of the recording of information, in response to binary information input which is input to a light source driving circuit 151, the laser beam is incident on a collimator lens 149 as pulse light of high and low levels and is converted to parallel light. The light after passing through the collimator lens 149 is reflected by a beam splitter 148, and is converged onto the magnetooptical recording medium 141. An initialization auxiliary magnet 143 acts to initialize a region before the recording of information in the magnetooptical recording medium 141 to which information is to be recorded by a power source 145 and a control circuit 144, in such a manner that the magnetic orientations of the auxiliary layer of the magnetooptical recording medium 141 are made uniform in the same direction at the positions of the rotation angle shifted from the recording beam position. Moreover, a recording magnet 146 provides a recording magnetic field having a polarity opposite to that of the initialization auxiliary magnet 143 to the position of the recording light beam, whereby information is recorded onto the recording layer of the magnetooptical recording medium 141.
On the other hand, in case of the reproducing operation, laser beam from the laser beam light source 150, which is weaker than at the time of the recording of information and is not subjected to modulation, is incident onto the collimator lens, and is converted to parallel light. The parallel laser beam is reflected by the beam splitter 148 and converged on the magnetooptical recording medium 141 by the objective 147. The light reflected by the magnetooptical recording medium 141 returns to the objective lens 147 and passes through the beam splitter 148. Then, after passing through the beam splitter 148 the light passes through a condenser lens 152. Then, the reflected light passes through a polarization analyzer 153 and is converged onto a photoreceptor 154. The polarization analyzer converts the reflected light to an intensity change depending on the rotation state of a polarization surface. As a result, an output of the photoreceptor 154 is output as a reproducing signal in response to the recording information.
However, with the optical card recording/reproducing apparatus described in the foregoing, the problem arises that the apparatus has a large size when the initialization auxiliary magnet and the recording magnet are simply mounted thereon.